In wireless devices such as cellular telephones and other full duplex transceivers, transmitter and receiver circuits are generally active simultaneously while sharing the same antenna. Bi-directional communication over a single transmission line is a standard method used in common wireless devices for navigating RF signals thereon. A standard method of connecting the RF antenna to a transmitter (Tx) and a receiver (Rx) includes connecting the antenna to a duplexer device. The duplexer connects the antenna to the transmitter for outgoing RF signals and the same antenna to the receiver for incoming RF signals. The duplexer prevents the incoming RF signals from reaching the transmitter and prevents the outgoing RF signal from reaching the receiver. Thus, the main goal of such a duplexer is to provide total separation between transmitting and receiving paths to/from a single common antenna and providing high isolation between the paths. FIG. 1A shows an example of a wireless device configuration using a duplexer.
FIG. 1B shows a transceiver block diagram including a duplexer with three connections: to an antenna, to a receiver and to a transmitter.
FIG. 1c shows an example of a physical duplexer device with three connection points—to the antenna, to the receiver and to the transmitter.
There are three major methods of realization for RF duplexers: using semiconductor switches, using RF magnetic devices and using a combination of band-pass filters usually built with SAW technology.
Duplexers with semiconductor switches (FIG. 2A) probably involve the simplest method for RF signal navigation. According to this method, the switch simply breaks the unwanted path allowing RF signals to propagate to the antenna from the transmitter (for outgoing signals) or allowing RF signals to propagate from the antenna to the receiver (for incoming signals). However, this method requires an external source of energy for the switch and a detector for incoming/outgoing direction recognition. Thus, while the breaking part itself is relatively simple, this method requires additional complicated active parts in addition to the energy source. This method is described, for example, in US U.S. Pat. No. 5,689,817 and in U.S. Pat. No. 6,351,628.
Another method for RF signal navigation includes using duplexer devices having magnetic material. This method is based on interaction between the RF signals and magnetic material inserted into the duplexer devices causing a Faraday Effect. Such an interaction causes phase change for the RF signals (FIG. 2B) and as a result, the signal always exits the port adjacent to its input port (FIG. 2C). Connecting the antenna, transmitter and receiver of a wireless device to different ports of such a duplexer may provide a fitting navigation of RF signals in certain applications. However, the magnetic duplexer has significant disadvantages:                a. high energy (insertion) losses due to presence of magnetic material (typically close to 2 dB);        b. it requires having a relatively large size;        c. its structure necessitates high costs.        
Such devices are described, for example, in U.S. Pat. No. 3,183,457 and in U.S. Pat. No. 2,887,664.
Another method for RF signal navigation includes using duplexer devices based on band pass filters containing two filters for two frequency bands since incoming and outgoing RF signals usually use different frequencies. Received signals from the antenna that “spill over” to the transmitter path are filtered out (i.e. blocked by the filter), as shown in FIG. 2D. However, even though the transmitted and received signal frequencies are different they are very close with small frequency separation, thus requiring filters with steep rejection. Such rejection can be obtained with SAW technology at the expense of high insertion loss (typically close to 2 dB). Isolation between the paths can also be a problem. Such a design is described, for example, in U.S. Pat. No. 5,864,260 and in U.S. Pat. No. 5,515,015.
Marketplace factors demand long battery life, low cost and high levels of performance. These aforementioned prior art methods still lack efficient means for providing sufficient RF signal navigation that overcome several of the aforementioned shortcomings. It is therefore an object of the present invention to provide an efficient duplexing means and method.
It is further an object of the present invention to provide a method and means to overcome the aforementioned shortcomings.
Other objects and advantages of the present invention will become apparent as the description proceeds.